The two giants of European football will meet in the first leg of their last-16 UEFA Champions League clash on Tuesday night.
The mouth-watering showdown also sees Old Trafford boss Sir Alex Ferguson go head-to-head with old adversary Jose Mourinho for the first time since the Portuguese coach parted company with Chelsea.
While Ronaldo knows the reigning Serie A champions must be respected, he insists that the Red Devils have the edge as Europe's premier club competition enters the knockout phase where there is no margin for error.
Experienced"From now on, all games are important," the Portugal international told uefa.com. "It's time to kill or be killed.
"Whoever loses will exit the competition and we don't want to lose, we don't want to get stuck along the way. It will be a difficult game, but I think that Manchester United have a better team, and we'll do our best to win it.
"They're a team we need to respect," he said. "They're a good side and first in Serie A so we need to be very careful.
"They're a team with very experienced players, but we also have our aces and great players. We have a more experienced team, we're the reigning champions.
"It will be a good game, a well-contested game, and the better team will win."
Ronaldo helped United lift the Champions League trophy last season as Ferguson's side overcame Premier League rivals Chelsea on penalties in Moscow.
EmotionThe gifted playmaker insists it is a moment he will never forget and he is eager to repeat the feat again.
He added: "I always had a great ambition to win the Champions League, because it isn't obtainable for every player. It was my first Champions League win, so the emotion was spectacular.
"I remember Edwin van der Sar saving Nicolas Anelka's penalty and for me it was like the earth stood still, it was a really brilliant sensation. Sometimes we can't control our emotions.
"It's every player's ambition to be a part of the Champions League, and they would all like to win it. I've had that privilege, and I hope to repeat that very soon."